In a chromatography, particularly in a high speed liquid chromatography, the internal diameter of the column has been required to become smaller and smaller because of increasing the separation rate, raising the microanalytic ability, enhancing the separating capacity, economizing the packing material and so on. Attempts of diminishing the internal diameter have been considerably advanced as far as practical use of columns having the internal diameter around 2.5 mm. However, further reduction of the dimension down to 1.0 mm or 0.5 mm has been hampered by the occurrence of the undermentioned disadvantages; in other words, effective reduction of the internal diameter has been, in fact, stalled.
A. The packing material packed inside the chromatographic column, usually particulate or solid layer, is stuffed in relatively close contact with almost uniform clearances between the particles, as shown in FIG. 1, but with some irregular or fairly large clearances, in relation to the inner surface of the column, which are called voids in this case. Although the clearances between the particles are nearly uniformly narrow or small, those voids between the particles located radially outermost and the inner surface of the column tend to be irregular or relatively large as shown with 3 in FIG. 1, which makes the passing rate of the eluent irregular or changeable and, in turn, conspicuously degrades the separating ability. The undesirable effect of the latter voids varies with the proportion between the column internal diameter and the particle size of the packing material; and it has been found that the decreasing of the column internal diameter below a certain value with respect to a certain value of the particle size of the packing material shows a critical degradation of the column function. This seems to be the greatest reason of preventing the reduction of the column internal diameter to below 1.0 mm. (b) The smaller the column internal diameter becomes, the greater becomes relatively the bad effect due to the minute flaws or cracks, tiny recesses or dents on the inner surface of the column, which bad effect appears in the local irregularities of the flowing speed of the liquid, consequently, in the degradation of separating ability.
This phenomenon is particularly inevitable when a particulate material of a substantially uniform particle size is used in relation to a column of a certain predetermined internal diameter. Confronting with the requirement of the gradual reduction of the column internal diameter, the above-mentioned difficulty has been a great problem to be solved. In order to alleviate the aforementioned unfavorable effect, enlarging the column internal diameter has been tried to improve the relative proportion with the particle size of the packing material, which directly contradicts the general trend of the gradual reduction of the column internal diameter and does not contribute to the solution of the problem at all.
The present invention, therefore, aims to provide a novel and practical column which has solved the difficult problem, wherein the cross-sectional area of the eluent path, even in a column having a very small internal diameter, is almost equal or uniform throughout the entire length of the column.